Method and apparatus for detecting anomalies in a meter movement

ABSTRACT

Method for detecting anomalies in the motion of the moving systems of electrical meters and similar devices including the steps of applying a ramp current to the meter movement to develop a ramp voltage across it and detecting perturbations in the ramp voltage. Embodiments of apparatus for practicing the method are also disclosed.

Einited States Patent Plake Sept. 25, 1973 METHOD AND APPARATUS FORDETECTING ANOMALIES IN A METER MOVEMENT William C. Plake, Santa Barbara,

Calif.

Inventor:

FOREIGN PATENTS OR APPLICATIONS 2,515,969 11/1965 Japan 324/74 PrimaryExaminer-Rudolph V. Rolinec Assistant ExaminerRolf Hille AttorneyRalphL. Cadwallader et al.

[5 7 ABSTRACT Method for detecting anomalies in the motion of the movingsystems of electrical meters and similar devices [52] US. Cl. 324/74,324/57 R including the Steps of pp y g a p rrent to the [51] Int. Cl.G01! 3/09, (3101! 35/00 meter movement to develop a mp oltage across it[58] Field of Search 73/l R, 32 /74, 57 R and detecting perturbations inthe p voltage. Em bodiments of a aratus for racticin the method are [56]References Cited also disclosed pp p g UNITED STATES PATENTS I 2,618,6863/1948 DeLange 324 57 R 7 Claims, 11 Drawmg Flgures TO M P vgfTAGE m l/i l/ UTILIZATION GENERATOR /2 A i COMPARATOR SYSTEM 20 26 2a 35 /4 T 52THRESHOLD VOLIAGE CONTROL INHIBIT LOGIC CIRCUIT PIJEMEU 3,761,812

SHEET 10F 3 I TO RAMP If I UTILIZATIO G E I I E I$/ST )R l I ICOMPARATOR SYSTEM THR OLD VOL GE CONTROL INHIBIT LOGIC CIRCUIT 35 33PATENTEUSEPZSIQYS SHEET 20F 3 l I. W f 52 40 48 50 RAMP DETECTORezaazxzisR Kl i2} l /4 154' W T I T 5 I P76 6 /6 r 6 VO LTAGE GENERATORRAMP METHOD AND APPARATUS FOR DETECTING ANOMALIES IN A METER MOVEMENTThe present invention relates to electrical meters and in particular tomethods and apparatus for determining whether the motion of the movingsystems of electrical meters, such as, for example, DArsonval typemeters, is faulty or not.

Some of the conditions that interfere with the normal turning of themoving system of an electrical meter are a warped or loosened scale,fibers extending upward from a paper scale, iron filings or otherobstructions in the air gap, a bent pointer or damping vane, a flatpivot or broken jewel, a moving system that is too tight or too loose inits bearings. All such conditions are hereinafter referred to asanomalies in the moving system.

The prior art teaches that some of these anomalies can be detected byobserving the jumping of the pointer as the operating current of themeter is very slowly increased or decreased to produce a gradual changein deflection. Further, during such testing, if the meter is set to ascale mark and the meter is lightly tapped, a slight change in theposition of the pointer reveals the presence of pivot friction. Suchtests require highly skilled personnel who are able to properlyinterpret their observations.

Thus, calibration procedures for electrical meters do not normallyinclude tests for determining the presence of anomalies. To the best ofmy knowledgeand belief, suitable test equipment for doing so reliablyand automatically has not heretofore been available. With the presentinvention I propose to fill that need.

Accordingly, it is an object of the present invention to providemethods, and apparatus that will serve to check the motion of movingsystems of various types of electrical meters and instruments, as wellas loudspeakers, accelerometers, etc., reliably and quickly and withmuch greater accuracy than with the techniques heretofore taught.

In accordance with another object of the invention, simple and reliableapparatus is provided for performing the desired methods with but a fewsimple steps which may be carried out under the control of nonskilledtesting personnel.

The invention contemplates in its main aspect applying a ramp current tothe meter movement thereby producing a ramp voltage across the terminalsof the meter. In the absence of anomalies in the motion of the movingsystem of the meter there will be no perturbations in the ramp voltage.However, if anomalies are present, perturbations in the ramp voltagewill be created and these are detected by several methods hereinafterdescribed in detail.

The invention, both as to its organization and method of operationtogether with further objects and advantages thereof will best beunderstood by reference to the following description taken in connectionwith the accompanying drawings, in which:

FIG. 1 illustrates schematically and partly in block diagram a preferredembodiment of the present invention;

FIGS. 2, 3, 4A, 48, 5A and 5B illustrate waveforms useful in explainingthe operation of the embodiment of FIG. 1;

FIGS. 6 and 7 illustrate other embodiments of the present invention; and

FIGS. 8 and 9 illustrate results obtained in testing several meters withthe embodiment of FIG. 6.

Referring to FIGS. 1 through 58, ramp current 10 derived throughresistor 12 from the ramp voltage, not shown, produced by generator 14and applied to meter 16, produces an IR drop across the internalresistance of meter 16. Concurrently, ramp current 10 causes the movingelement of meter 16 to rotate at a constant rate, in the absence ofanomalies in its motion. This may be shown as follows:

dO/dt k, k, where I magnitude of current in current ramp;

0 total angle through which the moving system rotates;

r time;

dO/dt angular velocity; and

k, and k are constants.

The constant angular velocity of the coil in a constant magnetic fieldcauses a constant CEMF to be induced in the coil of meter 16. Ifanomalies are present in the motion of the moving system, the angularvelocity will not be constant and voltage perturbations will appear inthe CEMF. The resultant voltage appears as voltage ramp 18 of FIG. 3 inwhich the IR drop is considerably larger than the CEMF, or any voltageperturbations occuring therein.

Capacitor 20 differentiates ramp voltage 18, producing voltage waveform22 which has a constant magnitude in the absence of anomalies in themoving system. If anomalies are present, voltage perturbations 24 occurin voltage waveform 22. The time duration of ramp current 10 may be madeas long as desired. Reasonable times, for test purposes, are from S to30 seconds. These time durations tend to assure that perturbationsoccurring in normal service will be detected.

Obviously, the perturbations in voltage waveform 22' may be observed onan oscilloscope or may be detected by other means. For employment in anutilization system the remainder of the embodiment of FIG. I may beemployed. This comprises amplifier 26 to amplify waveform 22 anddifferentiating capacitor 28 to differentiate the amplified waveform 22,producing voltage waveform 30 which has a zero level in the absence ofanomalies. Comparator 32 compares voltage 30 with a predeterminedthreshold voltage 34 and produces an output 36 whenever voltageperturbations 24 exceed threshold voltage 34. Voltage perturbations 24occur in voltage waveform 30' in the presence of anomalies. Output 36may be utilized by the utilization system in any manner desired. Ifdesired, comparator 32 may be inhibited by inhibit circuit 33, which maybe controlled automatically by control logic 35 during start-up andreversal of motion of the moving system of meter 16 to avoid falseindications of anomalies.

In the embodiment of FIG. 6, ramp current 10, derived through resistor12 from the ramp voltage, not shown, produced by generator 14 andapplied to meter 16, produces ramp voltage 18 across meter 16. The rampvoltage produced by generator 14 is also applied through resistor 40 toinverting amplifier 42, while ramp voltage 18 is appliedto amplifier 44.The output voltages of amplifiers 42 and 44 are ramp voltages ofopposite polarity. The moving system of meter 16 is then locked inposition so no CEMF is produced. The

gains of amplifiers 42 and 44 are so adjusted, and the values ofresistors 46 and 48 are so selected, that the output ramp voltages areconverted to ramp currents I and I of opposite polarity and equalabsolute magnitudes. Ramp currents I, and I then sum to zero at summingpoint 50.

The moving system of meter 16 is then unlocked. As before, the CEMFinduced in the coil will be constant and have no perturbations in theabsence of anomalies in the motion of the moving system. However, ifanomalies are present, they will appear as perturbations in the CEMF andas current perturbations at summing point 50 which are detected bydetector 52.

Detailed recordings may also be made of the input ramp voltage producedby generator 14 at terminals 54, 54' and of the CEMF present at summingpoint 50 at terminals 56, 56'. These recordings may have a number ofdifferent uses, such as production testing, nonlinearity detecting, ortest qualifications.

It will now be apparent to those skilled in the art that alternativelythe output ramp voltages of amplifiers 42 and 44 of FIG. 6 can beadjusted to have equal absolute magnitudes when the moving system ofmeter 16 is locked, and that amplifier 42 need not be an invertingamplifier. Then, with the moving system unlocked, the output rampvoltages may be compared by a comparator set to trigger when voltageperturbations occur in the output ramp voltage of amplifier 44. Othervariations can be made.

In the bridge embodiment of FIG. 7 generator 14 furnishes a ramp voltageto meter 16 through resistor 60 and to resistors 62 and 64. Resistors 60and 62 have equal resistances and resistor 64 has a resistance equal tothe resistance 66 of meter 16 when the moving system is locked. With themoving system unlocked, outputsignals from the bridge feed todifferential amplifier 68 as shown. As will be obvious to those skilledin the art of electrical measurements, other more complex and highlysophisticated bridge circuits may utilize the basic method of thepresent invention.

A Simpson Multimeter Model 260 was tested in the embodiment of FIG. 6and the outputs at terminals 54, 54 and S6, 56' were applied to an x-yrecorder to produce curves 70, 72, and 74 of FIG. 8. First, a rampcurrent was applied to the meter with its rotor locked producing thenearly straight line of curve 70. Curves 72 and 74 were produced withthe rotor unlocked and with ramp currents having time durations of 30seconds and 11 seconds respectively. Note that curves 72 and 74represent the CEMFs produced in the coil of the meter and that thecurves are relatively flat except when the pointer leaves the left stopand during portions 73 and 73' respectively. These latter portions ofthe curves clearly show the non-linearity of the meter when the pointeris at the upper end of the scale. Note also that hardly any voltageperturbations occur in these curves indicating that the motion of themoving system was not subject to anomalies.

FIG. 9 illustrates curves 80, 82, 84 and 86 produced by the embodimentof FIG. 6 in the same manner in testing four different Tripplet VOMs.Note, for example, that curve 84 has perturbation 88 which was notvisually observable when the ramp current was applied. Obviously, themeters that produced curves 84 and 86 have anomalies in the motions oftheir moving systems.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appendent claims, the inventionmay be practiced otherwise than as specifically described.

I claim: 1. A method of detecting anomalies in the motion of the movingsystem of an electrical meter or similar de vice, comprising:

applying a ramp current to the device to produce a ramp voltage acrossit; and

differentiating the ramp voltage to produce a DC voltage having aconstant magnitude in the absence of anomalies in said motion and a DCvoltage having perturbations in the presence of anomalies in saidmotion.

2. The method as in claim 1 further comprising the steps of:

amplifying the differentiated ramp voltage; and

differentiating the amplified differentiated ramp voltage to produce anoutput voltage having a zero level in the absence of anomalies andhaving perturbations in the presence of anomalies in said motion.

3. A method of detecting anomalies in the motion of the moving system ofan electrical meter or similar device, comprising:

inserting the device as one arm of a Wheatstone bridge, the other armsbeing resistors;

applying a ramp voltage to the bridge; and

adjusting the values of the resistance arms to produce a null balancewhen the meter movement is locked, output voltage perturbations beingthen produced when the meter movement is unlocked and during thepresence of anomalies in said motion.

4. Apparatus for detecting anomalies in the motion of the moving systemof an electrical meter of similar device, comprising:

circuit means for generating and applying a ramp current to the deviceto produce a ramp voltage across the device; and

means connected across the device for detecting perturbations in theramp voltage comprising a differentiating circuit connected across thedevice to differentiate the ramp voltage producing a DC voltage ofconstant magnitude in the absence of anomalies in said motion and a DCvoltage having perturbations in the presence of anomalies in saidmotion.

5. Apparatus as in claim 4 in which said detecting means furtherincludes:

an amplifier connected to the differentiating circuit for amplifying theDC voltage; and

another differentiating circuit connected to the amplifier fordifferentiating the amplified DC voltage to produce an output voltagehavinga zero level in the absence of anomalies and perturbations in thepresence of anomalies in said motion.

6. Apparatus for detecting anomalies in the motion of the moving systemof an electrical meter or similar device, comprising:

circuit means including a circuit for generating a ramp voltage and forapplying it across a first resistor and the device connected in seriesat a first node;

means for applying the ramp voltage across second and third resistorsconnected in series at a second node, the second resistor having aresistance equal in value to the resistance of the first resistor andthe third resistor having a resistance equal in value to 6 theresistance of the device when the moving sys- 7. Apparatus as in claim 6in which the perturbation mm locked posmon; and detecting meanscomprises a differential amplifier conmeans connected to detectperturbations in the voltage between the first and second nodes when themoving system is unlocked. 5

nected between the first and second nodes.

1. A method of detecting anomalies in the motion of the moving system ofan electrical meter or similar device, comprising: applying a rampcurrent to the device to produce a ramp voltage across it; anddifferentiating the ramp voltage to produce a DC voltage having aconstant magnitude in the absence of anomalies in said motion and a DCvoltage having perturbations in the presence of anomalies in saidmotion.
 2. The method as in claim 1 further comprising the steps of:amplifying the differentiated ramp voltage; and differentiating theamplified differentiated ramp voltage to produce an output voltagehaving a zero level in the absence of anomalies and having perturbationsin the presence of anomalies in said motion.
 3. A method of detectinganomalies in the motion of the moving system of an electrical meter orsimilar device, comprising: inserting the device as one arm of aWheatstone bridge, the other arms being resistors; applying a rampvoltage to the bridge; and adjusting the values of the resistance armsto produce a null balance when the meter movement is locked, outputvoltage perturbations being then produced when the meter movement isunlocked and during the presence of anomalies in said motion. 4.Apparatus for detecting anomalies in the motion of the moving system ofan electrical meter of similar device, comprising: circuit means forgenerating and applying a ramp current to the device to produce a rampvoltage across the device; and means connected across the device fordetecting perturbations in the ramp voltage comprising a differentiatingcircuit connected across the device to differentiate the ramp voltageproducing a DC voltage of constant magnitude in the absence of anomaliesin said motion and a DC voltage having perturbations in the presence ofanomalies in said motion.
 5. Apparatus as in claim 4 in which saiddetecting means further includes: an amplifier connected to thedifferentiating circuit for amplifying the DC voltage; and anotherdifferentiating circuit connected to the amplifier for differentiatingthe amplified DC voltage to produce an output voltage having a zerolevel in the absence of anomalies and perturbations in the presence ofanomalies in said motion.
 6. Apparatus for detecting anomalies in themotion of the moving system of an electrical meter or similar device,comprising: circuit means including a circuit for generating a rampvoltage and for applying it across a first resistor and the deviceconnected in series at a first node; means for applying the ramp voltageacross second and third resistors connected in series at a second node,the second resistor having a resistance equal in value to the resistanceof the first resistor and the third resistor having a resistance equalin value to the resistance of the device when the moving system islocked in position; and means connected to detect perturbations in thevoltage between the first and second nodes when the moving system isunlocked.
 7. Apparatus as in claim 6 in which the perturbation detectingmeans comprises a differential amplifier connected between the first andsecond nodes.